The invention relates to a nonvolatile memory cell comprising a phase change material to in contact with a heater layer, the contact region of reduced area, and methods to form this heater layer.
Phase-change materials such as chalcogenides have been used in nonvolatile memories. Such materials can exist in one of two or more stable states, for example a high-resistance and a low-resistance state. In chalcogenides, the high-resistance state corresponds to an amorphous state, while the low-resistance state corresponds to a more ordered crystalline state. The conversion between states is generally achieved thermally.
Conversion from one phase to another is achieved most effectively if the thermal energy is focused into a relatively small area. Some prior art devices have tried to focus thermal energy by forming a very small contact area using photolithography. The limits of photolithography, however, restrict the usefulness of this approach. A need exists, therefore, for a method to concentrate heat in a phase change memory in a volume smaller than that easily achievable using photolithography.